 A man questioned the Messenger of Allah ﷺ and said : Do you think that if I perform the obligatory Prayers, fast in Ramadaan, treat as lawful that which is Halaal, and treat as forbidden that which is Haraam, and do not increase upon that [in voluntary good deeds], then shall I enter Paradise?
He ﷺ replied: Yes

It was related by Muslim.

And the meaning of ‘treat as forbidden the Haraam’ is to stay away from it, and the meaning of ‘treat as lawful the Halaal’ is to perform it believing it to be permissible.

Explanation of Hadeeth Number 22

This man who questioned the Prophet ﷺ was an-Nu’maan bin Qawqal. The Shaykh Abu ‘Amr bin as-Salaah (rahimahu Allah) said: “What is apparent from his statement ‘treat as forbidden that which is Haraam’ is two issues. The first: that he believes those things to be forbidden. The second: that he does not perform those actions, which is different from the case of treating the Halaal as permissible, as in the latter case it is sufficient to believe that they are permissible [without actually performing all of them].”

The author of al-Mufham said that in this hadeeth the Prophet ﷺ did not mention to the questioner any of the voluntary actions, and this is a proof indicating the permissibility of leaving all of the voluntary actions. But the one who does so, and does not perform anything from the voluntary deeds, has deprived his soul of a tremendous profit and an immense reward. And the one who persists upon leaving something from the Sunnah is considered to have a deficiency in his Religion, and an impairment to his decency and justice. And if his leaving it is due to disdain or indifference to it, or due to his detesting it, then this is considered to be fisq (sinfulness) that is deserving of punishment.

And the leaders from amongst the Sahaabah (radiAllahu anhum) and those who followed them would persevere upon performing the voluntary deeds, and these would make easy persistence upon the obligatory deeds, and they would not distinguish between the voluntary and the obligatory in trying to attain reward.

And here the Prophet ﷺ left out the Sunan and other voluntary acts in his advice to the man to make the Religion easy for him, due to his having recently accepted Islaam, as excessive obligations may have alienated him from the Religion. And he ﷺ knew that if the man established himself upon Islaam and if Allah opened his heart to the Deen, then he would, of his own accord, seek those voluntary actions which the other Muslims sought. Also, it is possible that the Prophet ﷺ did not mention the voluntary deeds in his advice so that the man would not wrongly assume that such actions are also obligatory.

And similarly in another hadeeth:
A man asked the Prophet ﷺ about the Salaah (Prayer), so he ﷺ told him that they are five. So the man said: “Am I required to perform any more [other than these five]?” to which the Prophet ﷺ replied “No, except that which you perform voluntarily”. Then the man asked about the Fasting, and the Hajj and other prescribed matters, and the Prophet ﷺ answered him [in a similar manner]. Then at the end of this the man said : “By Allah, I will not increase upon this, nor will I perform less than it”, to which the Prophet ﷺ said : “He will be Successful if he is truthful”, and in another narration “If he holds onto that which he has been commanded with then he will enter Paradise”.

And the Sunan and voluntary deeds have been prescribed to complete and beautify the Obligatory deeds. So in the case of this questioner, and the one mentioned before him, the Prophet ﷺ did not include in his advice the voluntary deeds in order to make the Religion easy for them, until their own understanding of the Deen increased, which would then lead to a desire to attain the reward of the voluntary deeds.

So he who preserves the deeds obligatory upon him, and performs them in their time, without leaving anything from them or violating any of their requisites, then he will attain a tremendous and immense Success – may Allah grant us that. And similarly, he who comes with the obligatory deeds and then follows that up with additional voluntary deeds will achieve a Success even greater than the first.

Summary:

The hadeeth is self-explanatory and clear

That Paradise is guaranteed for him who fulfills his Prayer and Fasting in the right way, with faith and perfect submission, and without asscociating any partners with Him, together with treating as lawful those things that are so, and treating as forbidden those things that are so

That some things become an obligation to be done or avoided under certain circumstances and given certain conditions, and those things are included in the hadeeth too

That treating as lawful that which is lawful and treating as forbidden that which is forbidden essentially covers the practising of the whole of the Deen

That fulfilling the conditions of this hadeeth for Paradise is the upholding of Tawheed by the Worshipper in his life